Method for turning workpieces

ABSTRACT

DISCLOSED HERE ARE METHODS AND AUTOMATIC APPARATUS FOR GRINDING CYLINDRICAL WOEKPIECES, SUCH AS THE CONTOURED ROLLS USED IN METAL ROLLING MILLS. THE METHODS AND APPARATUS INVOLVE (1) AUTOMATIC FINDING OF THE LENGTHWISE CENTER OF ROLLS OF DIFFERENT AND UNDETERMINED LENGTHS SO AS TO ESTABLISH A REFERENCE POSITION FOR THE EXECUTION OF A NUMERICALLY PROGRAMMED PATH DEFINED RELATIVE TO THE CENTER OF A ROLL AS A POINT OF SYMMETRY, (2) THE STORAGE OF THE SUCCESSIVE INSTRUCTIONS OF THE MULTI-AXIS MOVEMENTS MAKING UP A NUMERICALLY DEFINED PROFILE OR CONTOURED PATH, AND THE USE OF THOSE INSTRUCTIONS REPEATEDLY AND IN WHOLE OR IN PART AS CALLED FOR BY DIFFERENT ONES OF A SEQUENCE OF COMMANDS READ FROM STORAGE AND EXECUTED IN SUCCESSION, (3) THE AUTOMATIC ALIGNMENT OF THE ROLL AXIS PARALLEL TO THE LONGITUDINAL AXIS OF MOTION IN A GRINDING MACHINE BY PIVOTING OF ONE END OF THE ROLL ABOUT THE OTHER UNTIL THE SENSED DIFFERENCE IN POSITIONS OF THE ROLL SURFACE, ALONG AN AXIS TRANSVERSE TO THE LONGITUDINAL AXIS AND AT LOCATIONS NEAR OPPOSITE ENDS OF THE ROLL, IS CHANGED TO A PREDETERMINED FRACTION ON THE ORIGINALLY SENSED DIFFERENCE, (4) THE INITIATION OF GRINDING PASSES FROM THAT END OF A ROLL WHICH IS LARGEST IN DIAMETER, AS AS TO AVOID &#34;DIGGING IN&#34; OR INCREASING THE DEPTH OF WHEEL BITE AS THE WHEEL MOVES LENGTHWISE OF THE ROLL, (5) THE EXECUTION OF CONTINUOUS PASSES OF THE GRINDING WHEEL WITH PRE-PROGRAMMED THICKNESS OF FEED RATE, WHEEL SPEED, ROLL SPEED, CONTINUOUS INFEED AND INCREMENTAL INFEED UNTIL A PRE-PROGRAMMED VALUES OF MATERIAL HAS BEEN REMOVED FROM THE ROLL SURFACE, AND (6) THE GRINDING DOWN OF A ROLL UNTIL IT IS REDUCED TO A DIAMETER EQUAL THAT OF A PREVIOUSLY GROUND ROLL OF A MATCHED PAIR. THESE FUNCTIONS ARE ALL OBTAINED BY THE CALLING OUT AND EXECUTION OF PRE-ESTABLISHED ROUTINES IN RESPONSE TO THE READING FROM STORAGE OF PRE-PROGRAMMED SEQUENCE COMMANDS, SO THAT IN THE DISCLOSED METHOD AND APPARATUS THERE IS AN AUTOMATIC PROGRESSION FROM EACH TYPE OF OPERATION TO THE NEXT, AND WITH THE FOLLOWING OF NUMERICALLY DEFINED PROFILE WHENEVER IT IS REQUIRED.

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1 AC/DC zamo cow-1mm DETECTOK ns PSL M19 PSR United Smtes Patent US. Cl. 51326 17 Claims ABSTRACT OF THE DISCLOSURE Disclosed here are methods and automatic apparatus for grinding cylindrical workpieces, such as the contoured rolls used in metal rolling mills. The methods and appa ratus involve (1) automatic finding of the lengthwise center of rolls of different and undetermined lengths so as to establish a reference position for the execution of a numerically programmed path defined relative to the center of a roll as a point of symmetry, (2) the storage of the successive instructions of multi-axis movements making up a numerically defined profile or contoured path, and the use of those instructions repeatedly and in whole or in part as called for by different ones of a sequence of commands read from storage and executed in succession, (3) the automatic alignment of the roll axis parallel to the longitudinal axis of motion in a grinding machine by pivoting of one end of the roll about the other until the sensed difference in positions of the roll surface, along an axis transverse to the longitudinal axis and at locations near opposite ends of the roll, is changed to a predetermined fraction of the originally sensed difference, (4) the initiation of grinding passes from that end of a roll which is largest in diameter, so as to avoid digging in or increasing the depth of wheel bite as the wheel moves lengthwise of the roll, (5) the execution of continuous passes of the grinding wheel with pre-programmed values of feed rate, wheel speed, roll speed, continuous infeed and incremental infeed until a pre-programmed thickness of material has been removed from the roll surface, and (6) the grinding down of a roll until it is reduced to a diameter equal that of a previously ground roll of a matched pair. These functions are all obtained by the calling out and execution of pre-established routines in response to the reading from storage of pre-programmed sequence commands, so that in the disclosed method and apparatus there is an automatic progression from each type of operation to the next, and with the following of numerically defined profile whenever it is required.

TABLE OF CONTENTS ABSTRACT OF DISCLOSURE 1 BACKGROUND OF THE INVENTION 2 SUMMARY OF THE INVENTION 2 BRIEF DESCRIPTION OF THE DRAWINGS 3 DESCRIPTION OF PREFERRED EMBODIMENTS 4 (A) An Exemplary Machine Tool 4 (B) Control Instrumentalities on the Grinding Machi 7 (1) Feedback pulse generators 7 (2) Steadyrest servomotor 7 (3) Sensing switches 8 (4) Probe assemblies 8 (5) Proximity switches 10 (C) The Control System in GeneraL. 10 (1) Contouring apparatus 11 (2) Sequence command system 13 (3) Data manipulation apparat 15 (D) Methods and Apparatus for Grinding a Roll 16 (1) Setup procedure 16 (2) Location of lengthwise center; M61 19 (a) Movement of the swivel base to the center of B axis travel 19 (b) Setting the platform 35 to the center of X axis travel. 20 (0) Movement of proximity switches to operative posi- 20 ons ((1) Movement of wheel to center of roll 21 (3) Automatic alignment of the roll axis 25 (a) Startup operations 26 (b) Movement to location of first gaging band 27 (c) Brilriging the wheel into touching contact with the 29 3,616,578 Patented Nov. 2., 1971 fice TABLE OF CONTENTS-@Ontinued (d) Grinding right gage band to predetermine depth. 30 (e) Movement of wheel to location of left gage band- 31 (f) Grinding of the left gaging band 31 (g) Retraction of the wheel free of the roll 32 (h) Sensing the location of the left gaging band on the rear side of the roll 33 (4) Determining direction of first grinding pass; initial grinding 39 (a) Right end larger 0 (1)) Left end larger. 41 (c) Status of the system prior to first grinding pass.- 42 ((1) First grinding pass and continuous passing 42 (i) Case I.-Material removal incomplete 4 (ii) Case II.Material removal complete 45 (5) Rough grinding 45 (6) Finish grinding 7 (7) Sensing and signaling the roll diameter 48 (8) Cleaning up the roll surface by sparking passe 53 (9) Polishing passes (E) Grinding a Second R011 to the Same Diameter" (F) An Alternative Embodiment BACKGROUND OF THE INVENTION The present invention relates in general to methods and apparatus for the turning of cylindrical workpieces, and while it will find advantageous use in the operation of lathes, the invention is adapted to be applied with special advantages in the operation of grinding machines for shaping or renewing the shape of rolls such as those employed in metal rolling mills.

In the operation of large installations for the rolling of steel or aluminum into thin sheets or strips for coiling, the high inter-roll pressures and roll speeds result in severe wear of the surfaces of the individual rolls. The wear is often non-uniform, and any roll surface irregularities result in magnified surface imperfections in the sheets or strips. It is common practice to change the rolls in a given mill stand frequently, as often as once per eight hour shift. When each worn roll is removed from the mill, there is a need to have its surface re-finished or re-ground to nearly perfect smoothness and with the desired cylindrical shape (which may be a convex or concave contour lengthwise of the roll to compensate for roll loading pressure and produce a desired cross sectional shape in the rolled strip). To keep a large mill, and the investment which it represents, operating efficiently, it is desirable to re-grind worn rolls not only quickly so that they may be returned to service, but also with precision.

The increasingly severe shortage of skilled machinists leads to the result that manual control of grinding machines offers little prospect of satisfying the current demand for rapid and precise grinding of rolls. The present invention aims to overcome that difficulty by making roll grinding operations substantially fully automatic through the use of pre-calculated, programmed data of two kinds, viz, profile data which define the contour of the finished roll surface, and sequence commands which call for the execution of different routines in succession, and with preselected operating parameters. The need for a machinist of extreme skill is thus obviated as the speed with which any roll can be completely reground is increased beyond that attainable by even the most skilled operator.

SUMMARY OF THE INVENTION A principal object of the invention is to provide methods and apparatus for the machining of cylindrical workpieces to desired contours and surface finishes by a succession of operations carried out automatically in sequence, and all defined in advance by programmed data. In particular, it is an object to utilize a program of successive instructions defining successive multi-axis movements which make up a desired contour or profile, and which may be followed in the machining of a plurality of workpieces which are to have the same finished profile; and in conjunction with such a profile program, to utilize a program of sequential commands, prepared individually for each workpiece or a group of identical workpieces so as to bring about the desired sequence of successive operations, including calling out and using all or a part of the profile program when that is required in the machining of the workpiece.

It is another object of the invention to facilitate the use of the same program of profile data in the shaping of surfaces of a plurality cylindrical workpieces such that the surface contours are symmetrical about the lengthwise centers of the workpieces, even though the exact length of any particular one of the workpieces is not known or measured and the axial placement of the workpiece in a numerically controlled grinding machine is not determined by a painstaking and time-consuming setup procedure. In this respect, it is a specific object to provide a method and apparatus for finding the lengthwise center of a workpiece, or to establish a zero reference for a numerical control contouring program at such center, quickly and preferably automatically after the workpiece has been placed in a machine tool.

A further object is to provide a new and advantageous method and apparatus for aligning the axis of a cylindrical workpiece parallel with the path of longitudinal movement of a tool in a turning machine. More specifically, it is an object to adjust the position of one end of a cylindrical workpiece in a direction transverse to the longitudinal motion of a tool, by utilizing the same sensor which initially detects misalignment, to sense and signal when the necessary corrective adjustment has been completed. A related object is to obtain quickly and preferably automatically the complete operation of sensing misalignment of a workpiece axis and adjusting the workpiece in a turning machine to align the workpiece axis, irrespective of whether the workpiece is initially cylindrical or tapered, i.e., has equal or unequal diameters at its opposite ends.

Another important objective of the invention is to provide for the sequential executive of different routines or operations in the overall shaping of a cylindrical workpiece, and wherein one or more routines so executed results in the removal of the desired thickness of material from the workpiece surface by successive passes of a tool to remove successive incremental thicknesses characterized by the advantages that the number of passes need not be estimated or commanded, and that the mere commanding of the removal of a desired thickness results in the automatic accomplishment of all of the individual operational steps, repeated as many times as as may be necessary, to effect such removal.

Still another object of the invention is to make it possible with speed and precision to turn down a cylindrical workpiece to a desired diameter, or to the same diameter as a previously turned workpiece so that two or more workpieces are matchedthis being characterized by a method and automatic apparatus which need not involve any special measurements or adjustments by a human operator.

The foregoing summary of the invention and the advantageous objectives achieved thereby will be better understood after consideration of the more detailed description of a specific, exemplary embodiment of the methods and apparatus. And additional advantages will also become apparent as the detailed description proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the attached drawings:

FIG. 1 is a fragmentary plan view, partly in diagrammatic form, of an exemplary grinding machine;

FIG. 2 is a vertical section taken substantially along the offset line 22 of FIG. 1;

FIG. 3 is a diagrammatic illustration of the spacial relationship of two probe assemblies and a roll in the grinding machine;

FIG. 4 is a diagrammatic cross section showing the basic organization of the two probe assemblies;

FIG. 5 is an end view, taken substantially along the line 55 of FIG. 4, of the rear probe assembly and showing the relationship of two proximity switches carried thereby;

FIGS. 6A and 6B, when joined to match the correspondingly labeled lines, constitute a block diagram of an exemplary control system associated with the grinding machine which is diagrammatically illustrated for ease of understanding;

FIG. 7 shows a typical workpiece or metal roll to be shaped in the grinding machine, and dimensions assumed by way of example merely for purposes of explanation;

FIG. 8 illustrates roll having unequal diameters at points spaced symmetrically from its lengthwise center, e.g., tapered, the axis of which is initially misaligned relative to the longitudinal path of wheel travel in the machine;

FIG. 9 is a fragmentary plan view of a roll having a convex profile, and with legends indicating the numerical programming of blocks of data to define the profile;

FIG. 10 is a block diagram illustrating apparatus which forms a part of the control system, and particularly that portion which processes signals to perform certain arithmetic functions;

FIG. 11 is a block diagram showing bidirectional counters associated with the front and rear probe assemblies, and devices for supplying input signals thereto or taking output signals therefrom;

FIG. 12 is a diagram, partly in schematic and partly in block form, showing the rear probe transducer and the manner in which its signal is utilized in aligning a roll axis in the grinding machine;

FIG. 13 is a block diagram showing the front probe transducer and the devices which respond to its signal;

FIGS. 14A through 14B are a series of simplified, diagrammatic plan views showing the position of the rear probe assembly at various stages in the routine of finding the lengthwise center of a roll placed in the machine;

FIGS. 15A through 15G, when joined to match the vertical lines L1 and L2 therein, collectively form a schematic diagram of control circuitry which is associated with the apparatus shown in FIGS. 6A and 6B to carry out various routines designated by sequence commands; and

FIG. 16 is a block diagram which when joined to FIG. 6A in lieu of FIG. 6B illustrates an alternative system embodying the apparatus of, and for carrying out the method of, the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS (A) An Exemplary Machine Tool Referring now to FIGS. 1, 2 and 6A, a grinding machine 20 is there shown as a specific example of the general class of machine tool which is to be controlled in the practice of the present invention, and the term grinding used herein is to be taken as a concrete example of the more generic term cutting which designates removal of material from a workpiece. Although the invention may be applied to good advantage in turning machines such as lathes having metal cutting tools for shaping generally cylindrical workpieces, the description which follows will refer for the sake of concreteness to the grinding machine 20 which has an abrading tool, specifically a rotationally driven grinding wheel 21, for shaping and finishing the surfaces of workpieces, such as metal rolls 22 of the type employed in rolling mills. Either when such a roll is first manufactured, or at frequent intervals during its useful life, it is necessary to shape and smooth the roll surface. The quality of the rolling mill product, and the efficiency of a rolling mill set-up require that the contour and surface finish of a roll be precise, and that the machining of the roll be effected in the shortest feasible time and with a minimum of skilled labor involving manual measurements or adjustments.

Most frequently, such generally cylindrical rolls are not to be shaped with a truly cylindrical surface, but are 

